mail() problem

Hi guys,
I'm trying to use the mail php function to send my subscribers emails like news, information, offers,etc.
The problem is when I test it on my system (Fedora 11 box and sendmail is up and running without changing any settings) I usually receive the mails after 4 or 5 hours and sometimes after 1 day. I googled it but I coundn't find something talking directly about it or even give a clear solution. I do know It's not the mail() problem but It's sendmail problem. Something not right in the config. I have some questions:-
1- If It's a sendmail problem, would you provide me with the solution?
2- Is the mail function can be used to send a large about of mails to the subscribers? and if It's not, Would you please suggest another way to send a large amount of mails?

1- If It's a sendmail problem, would you provide me with the solution?
2- Is the mail function can be used to send a large about of mails to the subscribers? and if It's not, Would you please suggest another way to send a large amount of mails?

Thanks alot for the help

Well, sendmail configuration depends on a lot of things that are clearly not mentioned here. Did you setup an SPF record for your domain? Are you trying to relay to another mail server? Does your domain name of the machine match the machine you're sending from? These could all hold you up from getting mail out quickly.

As to the "large number of mails", if you aren't bulk mailing people a bunch of trash then it could be that you're sending it too fast. Mail servers don't like rushes of mail all at once. You may need to slow down the timing of each individual send.

First of all, Thanks a lot for the reply.
I actually use the default configuration of the sendmail and the hosts file (/etc/hosts). I really don't know if that affects the speed of receiving or sending mails. I don't send mails to another mail server because I simply trying to use my localhost. I'm actually a newbie in Linux world, so if you can guide me or provide more info about how to setup sendmail properly, I would really appreciated.

I'm not trying to send bulk mails but I'm thinking about it like this, If I have about 5000 or more subscribers and of course more than one of them are trying to send invitations to their friends by importing the contacts list. I don't know if that should be considered a lot of emails or shouldn't?